Low Iron and Low Thyroid: A Link in Pregnant Women?

Iron deficiency and hypothyroidism—conditions that could cause problems for mothers and babies during pregnancy, but are easy to treat—may share a connection, a recent study1 from Belgium suggests.

When researchers from Saint-Pierre University Hospital in Brussels tested 1,900 women during the first three months of their pregnancy, they found that 35% were low on iron. Among them, 20% had subclinical hypothyroidism and 10% had elevated levels of thyroid perioxidase antibodies, a sign of immune-system damage to their thyroid gland. In contrast, 16% of women with normal iron levels had low thyroid function and 6% had high thyroid antibody levels. The study was published in the September issue of the European Journal of Endocrinology.

The researchers say it’s too soon to tell whether low iron contributes to hypothyroidism or whether hypothyroidism leads to low iron. Some research suggests hypothyroidism leads to low iron stores2 others suggest low iron may interfere with healthy thyroid functioning.3 Their next step: Checking whether the conditions affected the health of mothers and babies. They also plan to pursue the iron/thyroid association. For now, lead researcher Kris Poppe, MD, director of the Endocrine Clinic at Saint-Pierre University Hospital, says the study underlines the importance of iron testing for pregnant women and for women planning a pregnancy – and of eating an iron-rich diet and adding a supplement if recommended by your doctor.

"Women should be checked for iron deficiency during pregnancy, and ideally before, too. Supplements should be given out to decrease a number of established pregnancy complications, but it needs to be proven whether they can decrease thyroid problems,” Dr. Poppe says. "Considering that our study took place in a relatively wealthy country, our results show that even in 2016 iron deficiency remains an important problem."

Iron, Thyroid Hormones and Pregnancy

During pregnancy, a woman’s blood volume expands by 50% and the number of iron-rich, oxygen-carrying red blood cells swells by 25% —all to supply a growing fetus with oxygen, fuel and nutrients, according to the American College of Obstetrics and Gynecology. 4 As a result, a woman’s body needs twice as much iron as it did before pregnancy. According to the National Institutes of Health, a pregnant woman needs 27 mg of iron a day while a nonpregnant woman in her childbearing years needs 18 mg.5 Low iron levels can contribute to premature birth, low birth weights and even a higher risk for death. 6 In the United States, an estimated 18% of pregnant women have iron-deficiency anemia according to U.S. Preventive Services Task Force7 but the number may be as high as 50% according to the National institutes of Health.8

A developing fetus puts big demands on the mother’s thyroid, too. This butterfly-shaped gland in the neck grows by 10% and pumps out 50% more thyroid hormones during pregnancy. These hormones are important for brain development – especially early on, when a fetus isn’t producing its own. An estimated 2.5% of women of child-bearing age in the U.S. may have subclinical hypothyroidism – a number that may rise during pregnancy when greater demands are put on the thyroid, according to an American Thyroid Association’s taskforce on thyroid disease during pregnancy.9 Pregnant women with hypothyroidism may be at increased risk for miscarriage, preterm delivery and developmental problems for their baby. 10, 11 ACOG recommends testing for hypothyroidism in pregnancy only in women with symptoms (like severe fatigue, depression, joint and muscle pain, dry skin, brittle hair) or a history of thyroid problems.12

Routine blood tests early in pregnancy include iron checks that will show if you have iron-deficiency anemia. In fact, they’re recommended by ACOG as well as the American Academy of Family Physicians, the U.S. Preventive Services Task Force, and the Centers for Disease Control and Prevention. 13 According to ACOG, pregnant women should begin a doctor-recommended iron supplement in addition to a prenatal vitamin (which also contains iron) if iron deficiency anemia is confirmed. 14

It’s also smart to choose iron-rich foods before and during pregnancy. Women of childbearing age who have heavy menstrual periods may also be at risk for low iron. Top sources include fortified breakfast cereals, white and kidney beans, lentils, spinach, beef, dark-meat chicken, tuna and stewed tomatoes. Iron from meat, poultry and seafood is more easily absorbed—and can also boost absorption from plant foods.15

9. The American Thyroid Association Taskforce on Thyroid Disease During Pregnancy and Postpartum: Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum. Thyroid. 2011 Oct; 21(10): 1081–1125. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3472679/